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Week 3 Checkpoint: Functions, Files, and JSON — Python For Researchers

Day 22 · ~11 min●

Five days, five functions. make_table_row, summarize_group, parse_respondent_csv, load_respondents_from_csv, respondents_to_json. Which moment felt like a genuine upgrade?

load_respondents_from_csv replacing my manual split logic. I've been doing that by hand in R scripts for two years and never thought to look for a standard library solution.

Every language has a CSV reader that handles quoted fields. The manual split approach was a stepping stone — it showed you what DictReader automates. What about the JSON serialisation?

respondents_to_json completed the pipeline I could see in my head from Day 1: CSV text in, JSON summary out. That's the supplementary file for every paper I write from now on.

Supplementary materials generated by the same code that computed the stats. Reviewer 2's replication request just got a lot less terrifying.

Week 4 capstone is next. Ready to wire it all together.

Six questions — four from this week, two reviewing Weeks 1–2. Review questions marked [REVIEW].

Quiz

0/6

6 questions80% to passretry anytime

1.What does summarize_group(respondents) return when called without a group argument?

def summarize_group(respondents, group="all"):
    subset = respondents if group == "all" else [r for r in respondents if r["treatment_group"] == group]
    n = len(subset)
    ...
    return (n, mean_outcome, mean_age)

Stats for the 'all' group label onlyStats for every group separately as a dictStats computed over all respondents — the whole datasetAn error, because 'all' is not a valid treatment group name

2.What is io.StringIO used for in load_respondents_from_csv?

It converts the CSV text from UTF-8 encoding to ASCIIIt wraps the CSV string so that csv.DictReader treats it like an open file handleIt reads a file from disk and returns its contents as a stringIt compresses the CSV text before passing it to DictReader

3.What does n, mean, age = summarize_group(respondents, 'control') do?

Creates a list [n, mean, age] and assigns it to three names in sequenceUnpacks the tuple returned by summarize_group into three separate variablesCalls the function three times with different argumentsThis is a syntax error — Python cannot assign to three names from one function call

4.You call json.dumps({"control": {"n": 87}}). What type does the function return?

dictbytesstrNone

5.[REVIEW] A respondent dict has treatment_group: " Control " (with spaces). You pass it to group_by_treatment without cleaning first. Where does the respondent land?

In the 'control' bucket after Python auto-strips the spacesIn a new bucket with key ' Control ' (spaces included)It raises a KeyError because the key has invalid charactersIn the 'Control' bucket after Python auto-lowercases the key

6.[REVIEW] filter_eligible builds a result list using a for loop and append. Which alternative produces the same result in one line?

[r for r in respondents if r['age'] >= min_age][r >= min_age for r in respondents]respondents.filter(lambda r: r['age'] >= min_age)list(map(lambda r: r['age'] >= min_age, respondents))